1. Field of the Invention
The present invention relates to a plasma processing system and method, and more particularly to a plasma processing system and method with inductive coupling.
2. Discussion of the Background
Conventional plasma reactors used in semiconductor manufacturing have round parallel plate electrodes. A sample typically rests on a lower electrode and a plasma is formed above the sample to create reactive species to carry out deposition or etching operations. The power is coupled to the plasma capacitively.
For large area depositions, such as polycrystalline silicon deposition to form flat panel displays, it is difficult to use the round parallel plate reactors since larger area deposition requires larger electrodes which complicates the deposition process. Also, the machine becomes larger, greatly increasing its cost and the cost to use such a machine, since clean room floor space is very expensive.
A line plasma source has been developed, as described in application Ser. No. 08/383,495, the disclosure of which is herein incorporated by reference. A diagram of the source is shown in FIG. 1. A semiconductor wafer 20 with a top surface 20S is shown being transported in a transport direction (depicted by arrow 22) relative to plasma source 24 in a plasma reactor 25. Plasma source 24 includes a plasma chamber 30. Plasma chamber 30 includes walls for defining an essentially elongated narrow rectangular volume. Plasma chamber 30 includes chamber sidewalls 34SL and 34SR, and chamber top wall 34T. A face of plasma chamber 30 opposite chamber top wall 34T is open, forming a chamber outlet aperture. A plasma 44 is generated in the upper portion of the chamber and active species exit the chamber through a long, narrow xe2x80x9clinexe2x80x9d outlet where they react with a reactive gas or gas mixture on the sample surface. The sample is translated past the plasma line source and the film grows on the sample in a linear fashion. The power is applied to the reactor shown in FIG. 1 with an electric field applicator 50 encased in shield 52. The electric field applicator is positioned outside of the plasma chamber to couple an electric field through the plasma. Quartz windows 48 are disposed in the plasma chamber in the vicinity of the electric field applicator.
The above system has a problem when running at high power levels. The reactor has both current and capacitive components and at high power, and the capacitive component creates difficult problems for plasma reactors. At low frequency operation, the ions may develop significant kinetic energy from the applied a.c. field which may damage the electrodes or chamber walls and which may lead to contamination of the product. Typically the reactors are operated at higher frequencies so the ions cannot react to the a.c. field thereby to avoid collisions. However, operating the reactor at higher frequencies does not solve the problem. While the ions cannot follow the field reversal, a voltage develops between the plasma and the surroundings, termed the self-bias voltage. This DC voltage can accelerate ions into the walls resulting in chamber erosion, contamination of the work product and damage to the work product.
The line source is advantageous in forming large area polycrystalline silicon films. The problems described above occurs when forming such films since the depositions times are not short, increasing the possibility that some of the ions accelerated due to the self-bias will collide with the walls and/or with the product.
It is an object of the present invention is to provide a high power plasma reactor.
It is a further object of the present invention to provide a high power plasma reactor while eliminating, minimizing and/or controlling the self-bias voltage.
It is a further object of the present invention to provide a plasma reactor in a line configuration to treat large area substrates.
Another object of the present invention is to couple power inductively to a plasma while controlling capacitive power coupling to a selected amount.
These and other objects of the invention are achieved by a plasma processing system and method wherein a power source produces a magnetic field and an electric field, and a window disposed between the power source and an interior of a plasma chamber couples the magnetic field into the plasma chamber thereby to couple power inductively into the chamber and based thereon produce a plasma in the plasma chamber. The window can be shaped and dimensioned to control an amount of power capacitively coupled to the plasma chamber, and thereby enhance production of a particular plasma species within the chamber, by means of the electric field so that the amount of capacitively coupled power is selected in a range from zero to a predetermined amount. The amount of capacitive coupling is, however, quite small and does not significantly contribute to plasma formation. Also, a tuned antenna strap having r.f. power applied thereto to produce a standing wave therein can be arranged adjacent the window to couple magnetic field from a current maximum formed in the strap to the interior of the chamber. A desired amount of magnetic field and/or electric field coupling can be produced by arrangement of the chamber window adjacent that portion of the antenna strap exhibiting the desired current and voltage relationship. The window may have slots and/or apertures, the size and shape of which may be variable.
The window may be integrally formed in a wall of the plasma chamber. It is also advantageous to form a cooling conduit in the window to cool the window during plasma processing.
The system according to the invention is advantageously applied to a line source configuration. The invention may also be applied to a cylindrical plasma chamber and a cylindrical power source. Such a configuration is compact and easily handles plasma processing pressures. The cylindrical source may be also used in a scanning configuration where the source is scanned in order to produce a sample compared to scanning a sample across a fixed source. In the cylindrical configuration a coil may be embedded in a dielectric or quartz member and an electric field window serving as a window may be disposed about the coil.
According to the present invention there is also provided a method of plasma processing, including generating a magnetic field and an electric field; coupling the magnetic field into a plasma chamber to couple power inductively into the chamber and thereby produce a plasma in the plasma chamber; and controlling an amount of power capacitively coupled to the plasma chamber by means of the electric field so that the amount of capacitively coupled power is selected in a range from zero to a predetermined amount. In a preferred embodiment the method includes coupling power substantially only inductively by blocking substantially all of the electric field entering the chamber based on the shape and dimensioning of a window in the wall of the chamber. In this embodiment, the window maybe shaped and dimensioned to pass only a selected amount of the electric field to allow a desired amount of capacitive coupling to the plasma to tune the plasma chamber for production of desired plasma species. The amount of power introduced by capacitive coupling to the interior of the chamber is nevertheless quite small, and does not appreciably contribute to plasma formation. In another embodiment, the method includes generating substantially only a magnetic field to be coupled into the chamber in the vicinity of a chamber window using a tuned strap antenna in which a standing wave is produced and having a current maximum arranged adjacent the window. Alternatively, where it is desired to couple some electric field into the chamber, the chamber window can be arranged adjacent a portion of the strap in which current and voltage have a predetermined relationship to couple a desired amount of magnetic field and electric field into the chamber.